The guards hesitantly agree to let you explore the tunnel up ahead. The gate cracks open enough for you to slip through, but closes again behind you. The tunnel is fairly dark, traveling straight for about forty yards before curling down and to the left. You make your way forward, listening for the sound of hissing, but do not hear anything.
After several minutes you've crept about two hundred yards into the tunnel and start to feel a bit foolish. For all you know, the attack has started at a different gate and now you'll be trapped outside the cavern, unable to help, and unlikely to be able to defend yourself should a group of lizards find you. To say nothing of finding your way out.
As you turn to head back, a soft, echoing sound reaches your ears. You freeze in place, listening hard. It's not hissing, but also not human. Your eyes strain in the darkness, but far away you spot an unmistakably large creature headed for you. It's the Big One, and for some reason it's traveling all alone.